This invention relates to integrated circuits which provide timing and supply bias to logic circuitry.
It is often required to utilize integrated circuits in applications where the operating supply for the circuit contains a great deal of noise and electrical transients. This is especially true of the automotive environment where sensitive electronic circuitry has to function properly on the same supply lines with electrical spike producing elements such as relays, solenoids, etc.
It is normal practice to filter the supply line with a low pass filter consisting of a series resistor and a shunt capacitor to eliminate the effects of these transients. This, of course, adds additional cost to the electronic function. If one considers the increasing numbers of electronic functions appearing in the modern automobile, multiplied by the millions of automobiles manufactured annually, it is seen that the addition of one capacitor becomes a significant cost factor.
The objective of this invention is to eliminate the need for this capacitor by utilizing a capacitor already required in the timing section, to serve a second function as a power supply bias filter capacitor.
FIG. 1 is a simplified block diagram of a circuit of the prior art. The timing function of the circuit is provided by an oscillator formed by a comparator 10, a switching transistor 53 and a timing capacitor 14. The comparator 10 has an input 51 connected to a terminal 12 and a second input 55 connected to receive a reference signal from a conventional switched hysteresis circuit. The reference signal thus alternates between a lower threshold and an upper threshold. The terminal 12 is provided for connection to the timing capacitor 14 A switching transistor 16 is controlled by the comparator 10 to charge and discharge the capacitor 14 thereby generating a clock signal at the output of the comparator 10. The timing capacitor 14 is repeatedly charged through a resistor 18 until it reaches the upper threshold and is discharged through the switching transistor 16.
This circuit also includes logic circuitry 20. A commonly used technology for the logic circuitry is known as I.sup.2 L. This logic is modelled in the schematic as a diode 20. The logic may perform any number of different electronic functions, but the particulars of the logic circuit are not relevent to this invention. The invention is essentially concerned with supplying the necessary bias currents and voltages to whatever logic circuitry is being represented by the diode 20. The logic circuits may consist of a string of flip-flops acting a counters that are clocked by the oscillator clock signal. Current for operating the logic circuitry is provided through a resistor 22.
The supply of current for the timer and logic circuitry of this circuit is provided through a supply pin 24. A regulator 26 receives the supply from the pin 24 and provides current to the timer, the logic circuitry and any other remaining support circuitry on the integrated circuit. The supply pin 24 is connected to a voltage source 28 such as a battery via a low pass filter formed by a resistor 30 and a capacitor 32. In this prior art design, the capacitor 32 ensures that under transient conditions, where the battery supply may momentarily drop, current is still available to prevent loss of the logic circuitry's memory state. It is an object of the present invention to provide such an integrated circuit which does not require the capacitor 32.
The remaining components in FIG. 1 including the resistor 34 and the current mirrors formed by diode 36, transistor 38 and transistor 40 are merely shown to demonstrate that additional circuitry may be included in the integrated circuit which receive power from the regulator 26.